The present invention relates to an arm device adapted to move and position a first basic part relatively to a second basic part, said arm device comprising at least three arms capable of being extended and shortened in a controlled manner, and the arms are free to pivot in their attachments on the second basic part, while one attachment on the first basic part is rigid, and one of the arms is torsionally rigid. Such a device is known from Norwegian acceptance print No. 148216. As examples of the use of such an arm device are mentioned industrial robot, drilling rig for tunnels and mines, adjustment device for aerials.
As further examples of known technique are mentioned:
U.S. Pat. No. 3,215,391 shows an arm device capable of being used for for instance adjustment of the position of an aerial, which, thus, constitutes one of the basic parts, while the other end of the arms is fastened to for instance a plate or similar, which may be stationary or for instance fastened to a vehicle. The arms are rigidly attached in each basic part, and are constituted by telescopic arms having universal joints at the middle. This permits that one of the basic parts can pivot about two of the universal joints relatively to the second basic part, and the pivotal movement is controlled by extension or shortening of that arm whose universal joint is not situated along the pivot axis. Moreover, it is possible to displace the basic parts parallelly to each other, by extending and shortening the arms. Thus, the possibilities of moving the basic parts mutually are very restricted.
U.S. Pat. No. 3,374,977 shows a similar arm device, being adapted for aerial adjustment. The device comprises four arms being fastened with their ends to two basic parts. Said four arms, which can be extended and shortened and have universal joints at each end, have attachments at the corners of equally large squares, and a fifth arm having a fixed length and universal joints at each end is fastened to the basic parts at the center of said squares.
The basic parts can be freely adjusted with respect to mutual direction, but the mutual adjustment is restricted, in that the fifth arm maintains a fixed distance between the middle portions of the basic parts. At least two of those arms that are capable of changing their length must be actuated simultaneously. Moreover, the arm device is statically indetermined, and is not torsionally rigid, when the arms have equal lengths.
U.S. Pat. No. 3,288,421 also shows an arm device adapted to move a basic part relatively to another, and permits both a mutual angular adjustment and parallel displacement. The device comprises six arms, and the ends of two by two arms are journalled in the same pivot point, whereby the arms stand in a zigzag pattern between the basic parts. The device presupposes that both of the basic parts have a relatively large area, and the number of arms is relatively large. The mutual movement of the basic parts is very restricted.
Said Norwegian acceptance print No. 148216 shows a tool at the free end of the arm device. Said tool, which may of course be of a different structure than that shown in the print, is rigidly mounted on the first basic part, and can consequently only perform movements determined by the movements of said basic part. For some applications the possibilities of movement of the tool are too restricted. Said basic part, and consequently also the tool, are rigidly connected to the end of one arm and can, therefore, only perform pivotal movements about the other basic part, about the pivotal mounting of said arm on the other basic part, possibly combined with movement towards or from the other basic part. In other words the tool always follows all the movements of the first basic part.